Electromagnetic shields are known. The problems encountered in an assembly environment are also known. The importance of such shields and the severity of the assembly problems have increased with the relatively recent reduction in the physical size of underlying electronic assemblies that rely on such shields and the move to and acceptance of automated surface mount technology for such assemblies. With the advent of reduced size automated surface mount technology the electromagnetic shield is now required to meet stringent coplanarity specifications, occupy a minimum amount of physical space, be assembly efficient, and of course economically effective.
Reduced size goals for the assembly mandates minimizing the size of all components and the space between components as well as minimizing part counts. As a result of these space reductions the degree of shielding required may have increased since circuits and components that historically did not need to be isolated may now have to be in order to operate satisfactorily. This coupled with the historical fact that electromagnetic shields are among the larger components in an assembly has caused practitioners to direct significant attention to reducing the effective size of such shields. Assembly efficiency ordinarily mandates minimal part counts with 1 component being favored over 2 components, etc. In addition automated assembly requires a regular shaped component that is easily and repetitively handled by mechanically actuated assembly arms and this favors relatively regular exterior surfaces with a minimal amount of assembly motion directed to orientation.
The coplanarity requirements are derived from the fact that usually the assembly has a carrier, typically a printed circuit board, with a planer surface on which the various components are placed during assembly. Assembly usually includes placing the component on the planer surface in contact with a small amount of solder paste which is subsequently reflowed thus securing the component to the planer surface when the solder re-solidifies. The coplanarity specification intends to specify the extent to which the mounting surface of a given component complies with or corresponds to the planer surface to which it will be assembled. Minor deviations from the specification may result in major, probably fatal, flaws in the quality and integrity of the final assembly since the component will not be adequately secured to the planer surface.
It is known to use electromagnetic shields that resemble an open sided box. Careful control of the manufacturing process results in a shield that satisfies realistic coplanarity specifications. If multiple items need to be shielded, two shields can be employed however this may result in excess physical space being used as well as multiple piece parts. A single piece shield could be constructed that has a soldered or spot welded partition however such a shield while minimizing parts count has proven to be extremely difficult and thus costly to manufacturer in sufficient quantity and in compliance with reasonable coplanarity specifications.
Clearly a need exists for a cost effective electromagnetic shield that complies with required coplanarity specifications and lends itself to reduced size automated surface mount assembly operations.